is brake disc size limited by grip?

White Noise · Mr Dudwee Joined: 17 Dec 2004 Karma :

I have just been thinking about this and wonder if anyone has any answers.
It is pretty straight forward that the bigger diameter disc that you have on your brakes the more stopping power you have, due to having more material on the disc to grip per rotation of the wheel, my question is there a limit to the diameter of discs other that the diameter of the wheel? does having larger disc's increase the chances of locking up due to the fact that they will easily overcome the grip of the tyre.
Cheers
WN
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cagiva gezzer · World Chat Champion Joined: 17 Mar 2003 Karma :

Looking at it the wrong way. Bigger discs have more stopping power due to having more leaverage on the wheel.
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Mr.Everready · World Chat Champion Joined: 28 Mar 2003 Karma :

The Buells have rim mounted disks.

Dont know if theyre any better than normal.
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White Noise · Mr Dudwee Joined: 17 Dec 2004 Karma :

haGGard · Nearly there... Joined: 13 Oct 2004 Karma :

Im making a complete guess here, but i think the size of the front disk varies depending on the Power/Weight of the bike. For example, if you fit a massive disk brake to a scooter, it would stop if quick, but there is a much higher chance of locking up/doing accidental stoppies? Confused

I guess if you fit a disk that it too small, braking distances will be increased, especially if the bike is heavy, and there will be a greater chance of warping the disk as it will be under greater stress...

I think you have to find a decent comprimise between too big, and too small.

^^Probably all wrong but as i said, i just guessing/assuming Razz

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Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Main reason for larger disks is a larger surface area to disapate heat more quickly.

All the best

Keith
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paulyzf600 · Scooby Slapper Joined: 24 Oct 2004 Karma :

There would'nt be more material contact unless the calipers and pads are bigger like said above it's down to more leverage.

When I modded cars a few years ago I put bigger disc's on the front end and the stopping power at lower speeds was more or less the same but higher speeds the stopping power was 100% better but yes it was easier to lock the front of the car up as the brakes don't need to work harder to stop the wheel.
Also as Keith said bigger disk's help for better heat transfer.
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Kram · World Chat Champion Joined: 20 Oct 2004 Karma :

i rode an XJR400 for about a week, with racing discs / calipers / pads on the front end....
it was hell to stop. move the lever [---] < that far, the back wheel was off the ground (at speed)
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Frost · World Chat Champion Joined: 26 May 2004 Karma :

It's all about the setup of the bike. The designers set the calipers, and levers up so that you have control aswell as stopping power.

for example bikes with bigger discs and bigger pads normally have more pitons in the calipers to ditribute the fluid pushed down to them more. this means that a big lever movement results in a smaller movement at the pads than normal, giving you better control. Bikes that have better braking systems also tend to have grippyer tyres to help stop sheels from locking.

If engineers wanted to make brakes which would lock the wheel with zero effort, then they could. What they want to make is controlable systems that allow you to stop as fast as possible without locking the wheel.

Retro-Man · Traffic Copper Joined: 21 Aug 2004 Karma :

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Another point being that a larger disk will pass through the pads more quickly (the wheel is still rotating at the same speed, but being further out the disk has a larger circumferance to go through in the same time) so will generate more friction.

All the best

Keith
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